efi: Move most of efi_device_path into lib/efi

Most of these utility functions are useful for the app, so move them
into the common directory.

Move the GUIDs used by this file from their various other location, so
they are available to the app, even if it doesn't enabled EFI_LOADER

Fix the rather large number of checkpath warnings in this file, except
for the lwip one, best left to the maintainer to sort out.

One noteable change is adding a return value to dp_fill() for the case
where an option is not enabled but its uclass is referenced. This
presuambly never happens during execution, since if the uclass is not
supported there can be no device in that uclass and therefore nothing
will ever request its path. So just handle this like an invalid device.

Signed-off-by: Simon Glass <sjg@chromium.org>

lib/efi/Makefile

@@ -4,3 +4,4 @@
 #
 
 obj-y += basename.o
+obj-y += device_path.o